diff --git a/repos/gems/run/depot_autopilot.run b/repos/gems/run/depot_autopilot.run
index 060a31fe4e..bbc8c0cac3 100644
--- a/repos/gems/run/depot_autopilot.run
+++ b/repos/gems/run/depot_autopilot.run
@@ -456,7 +456,7 @@ proc prepare_to_run_genode { } {
 	set serial_id -1
 	set timeout 40
 
-	append qemu_args "-m 800 -nographic "
+	append qemu_args " -nographic "
 }
 
 
diff --git a/tool/run/power_on/qemu b/tool/run/power_on/qemu
index 39bc704c0b..48cd20f0e2 100644
--- a/tool/run/power_on/qemu
+++ b/tool/run/power_on/qemu
@@ -124,28 +124,33 @@ proc run_power_on { } {
 
 	# on x86, we support booting via pxe or iso/disk image
 	if {[have_board pc]} {
-		if {[have_spec okl4]} {
-			# okl4 system integration specifies RAM from 32 to 800 MiB
-			set qemu_ram 800
-		} else {
-			set qemu_ram 512
-		}
 
-		if {[regexp -- {-m} $qemu_args dummy]} {
-			set qemu_ram [regexp -inline {\-m.[0-9]+} $qemu_args]
-			set qemu_ram [regexp -inline {[0-9]+} $qemu_ram]
-		}
-
-		if {[have_spec okl4]} {
-			if {$qemu_ram < 800} {
-				puts "Configured memory ($qemu_ram) for OKL4 on Qemu must be at least 800M\n"
+		if {[regexp -- {-m\s+} $qemu_args dummy]} {
+			# can be -m 1024 or -m 1024G or -m size=1024G
+			set qemu_ram [regexp -inline {\-m\s+\S+} $qemu_args]
+			if {![regexp {([0-9]+)([MG]?)} $qemu_ram dummy qemu_ram ram_unit]} {
+				puts "Cannot parse memory argument ($qemu_ram)\n"
 				exit 1
 			}
+
+			if { $ram_unit == "G" } {
+				set qemu_ram [expr {$qemu_ram*1024}] }
+
+			if {[have_spec okl4]} {
+				if {$qemu_ram < 800} {
+					puts "Configured memory ($qemu_ram) for OKL4 on Qemu must be at least 800M\n"
+					exit 1
+				}
+			}
+		} else {
+			##
+			# append memory argument if not present, 800M is a sane default because:
+			# - 800M is minimum for OKL4
+			# - 768M is required for certain test cases (#3387)
+			#
+			append qemu_args " -m 800 "
 		}
 
-		append qemu_args " -m $qemu_ram "
-
-
 		if {[have_include "load/tftp"]} {
 			append qemu_args " -boot n -tftp [run_dir] -bootp boot/pulsar -no-reboot -no-shutdown "
 		} else {